1. Field of the Invention
The present invention generally relates to a method for fabricating an electrode of a plasma chamber, and more particularly to a method for fabricating a cathode electrode of a plasma chamber which is used for a thin film forming process or an etch process. The cathode electrode has a plurality of fine through holes formed by an ultrasonic technique and allows introduced gases to be dispersed into the chamber and additionally the surface flatness and hardness to be improved.
2. Description of the Related Art
Generally, in order to fabricate semiconductor devices using a silicon wafer as a substrate, various kinds of processes such as oxidation, diffusion, deposition, etch, photolithography, and ion implantation are essentially performed. Especially, deposition and etch processes are generally performed using plasma technologies.
When plasma technologies are applied in fabricating semiconductor devices, reaction gases within a process chamber are transformed into excited plasma gases by applying a radio frequency voltage to electrodes. The excited plasma gases react with a surface of a substrate, whereby thin film is deposited on the substrate or the surface of the substrate is etched.
With reference to FIG. 1, there is described a conventional plasma etch apparatus which is used for etching a surface of a silicon wafer. A cathode 14 and an anode 18 to each of which a radio frequency voltage 12 is applied are respectively disposed at an upper portion and a lower portion of a process chamber 10. In addition to the role as electrode, the anode also functions as a chuck to fix a wafer 16. A gas supply tube 26 for supplying an etch gas of a fluorine system and a circulation tube 20 through which cool water for cooling the heated cathode 26 circulates are respectively coupled to the cathode 14. A vacuum pump 22 is disposed at one side of the bottom portion of the chamber 10 and controls an ambient pressure of the chamber 10.
Gases which are supplied into the inside of the chamber 10 are ionized by a potential difference between radio frequency voltages respectively applied to the cathode 14 and the anode 18 and whereby they are transformed to plasma gases. The plasma gases react an upper surface of the wafer 16 to etch predetermined portions of the wafer 16.
In the above constituted plasma apparatus, an ambient condition such as a vacuum pressure, of the inside of the chamber 10 depends on performance of the vacuum pump 22 and cooling of the cathode 14 is performed by concurrently supplying cool water through the circulation tubes 20.
Referring to FIG. 2, the cathode 14 is made of a circular silicon plate and has a plurality of fine through holes 24 which are formed for the purposes of injecting the supply gases into the inside of the chamber 10. The plurality of fine through holes 24 are formed by a diamond drill.
In most of the semiconductor device fabrication processes, dirt particles are one of the most significant factors that determine production yield and are a very important checking item for all equipments used in the semiconductor device fabrication. However, the conventional cathode 14 has a drawback in that the fine through holes 24 of the cathode 14 act as a generating source of particles because the fine through holes 24 have inner wall and inlet portions that are very rough. In other words, while the reaction gases are supplied into the inside of the chamber 10 through the fine through holes of the cathode, particles are generated from the inner wall and inlet portion of the fine through holes 24 and are supplied into the inside of the chamber 10, whereby a process yield is lowered.
Accordingly, it is an object of the present invention to provide a method for fabricating an electrode of a plasma chamber capable of preventing particles from being generated from inner wall and inlet portion of the fine through holes formed in the electrode by forming the fine through holes using an ultrasonic technology.
To accomplish this object and other advantages, according to one aspect of the present invention, there is provided a method for fabricating an electrode of a plasma chamber. The method comprises the steps of: providing a circular silicon substrate facing a drilling plate having a plurality of tips projected from one surface of the drilling plate; supplying a polishing material containing a plurality of polishing particles on the circular silicon substrate and the drilling plate; and drilling a plurality of holes in the circular silicon substrate by colliding the plurality of polishing particles to selected portions of the circular silicon plate using an ultrasonic vibration of the tips of the drilling plate.
According to another aspect of the present invention, there is provided a method for fabricating an electrode of a plasma chamber comprising the steps of: providing a circular silicon substrate facing a drilling plate having a plurality of tips projected from one surface of the drilling plate; supplying a first polishing material containing a plurality of polishing particles on the circular silicon. substrate and the drilling plate; drilling a plurality of holes in the circular silicon substrate by colliding the plurality of polishing particles to selected portions of the circular silicon plate using an ultrasonic vibration of the tips of the drilling plate is performed by oscillations of an ultrasonic converter coupled to the other surface of the drilling plate; lapping the circular silicon plate to a first roughness using a lapping material; etching the circular silicon plate using an etch solution; polishing the circular silicon plate to a second roughness lower than the first roughness using a second polishing material; and cleaning the circular silicon plate.
It is preferable that the first polishing material has a roughness of 9 Moh or more.
It is preferable that the lapping material contains aplurality of lapping particles, the lapping particles having a diameter of 6-7 xcexcm.
The lapping material is one selected from a group consisting of silica, silicon carbide, alumina or zirconium.
It is preferable that the etch solution is one selected from a group consisting of potassium hydroxide, nitric acid, and hydrochloric acid.
The second polishing material contains a plurality of polishing particles, the polishing particles having a diameter of 0.1 xcexcm or less. The second polishing material is one selected from a group consisting of silica, silicon carbide, alumina, and zirconia.
It is preferable that the cleaning step comprises the steps of: dipping the circular silicon substrate in which the lapping step is completed in a first cleaning solution wherein oxygenated water is added to a heated ammonia water; dipping the circular silicon plate in a second cleaning solution wherein oxygenated water is added to a heated sulfuric acid; and cleaning the circular substrate by deionized water.